A Novel Mitogen-Activated Protein Kinase Docking Site in the N Terminus of MEK5α Organizes the Components of the Extracellular Signal-Regulated Kinase 5 Signaling Pathway

Abstract

The alternative splicing of the mek5 gene gives rise to two isoforms. MEK5␤ lacks an extended N terminus present in MEK5␣. Comparison of their activities led us to identify a novel mitogen-activated protein kinase (MAPK) docking site in the N terminus of MEK5␣ that is distinct from the consensus motif identified in the other MAPK kinases. It consists of a cluster of acidic residues at position 61 and positions 63 to 66. The formation of the MEK5/extracellular signal-regulated kinase 5 (ERK5) complex is critical for MEK5 to activate ERK5, to increase transcription via MEF2, and to enhance cellular survival in response to osmotic stress. Certain mutations in the ERK5 docking site that prevent MEK5/ERK5 interaction also abrogate the ability of MEKK2 to bind and activate MEK5. However, the identification of MEK5␣ mutants with selective binding defect demonstrates that the MEK5/ERK5 interaction does not rely on the binding of MEK5␣ to MEKK2 via their respective PB1 domains. Altogether these results establish that the N terminus of MEK5␣ is critical for the specific organization of the components of the ERK5 signaling pathway.The mitogen-activated protein kinase (MAPK) signaling pathways regulate numerous physiological processes during development and pathogenesis (10). They consist of the sequential activation of protein kinases that include a MAPK, a MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK or MKK) and a MEK kinase (MEKK) (10). At least four MAPK subfamilies have been identified: ERK1/2, ERK5, c-Jun NH 2 -terminal protein kinases (JNKs), and p38 MAPKs. MAPK activators include MEK1 and MEK2 for ERK1/2, MEK5 for ERK5, MKK4 and MKK7 for JNKs, and MKK3 and MKK6 for p38 MAPKs. MEKs/MKKs activate MAPK by dual phosphorylation on threonine (T) and tyrosine (Y) residues within a T-X-Y motif. A conserved cluster of two to five basic residues identified in the N terminus of MEK1 and -2 and MKK3, -4, -6, and -7 constitutes a consensus MAPK binding site that is necessary for the transmission of the signal (1, 28). A similar motif has been identified by sequence homology in MEK5, but its function as a docking site for ERK5 has not been proven (28).The ERK5 signaling pathway regulates by phosphorylation the activity of a number of transcription factors including myocyte enhancer factor 2 (MEF2) (12, 13). Consistent with its role in stimulating gene expression through the regulation of MEF2 activity, ERK5 contributes in vitro to regulating muscle differentiation and neuronal survival (6,16,24). The analysis of mutant mice in which the erk5 gene can be conditionally deleted has provided in vivo genetic evidence that ERK5 mediates the survival of endothelial cells (9). The loss of endothelial survival may be responsible for the cardiovascular defects observed in erk5 Ϫ/Ϫ and mek5 Ϫ/Ϫ embryos (21,25,29,32). Being twice the size (815 amino acids) of the other MAPKs, ERK5 possesses a unique C-terminal tail that contains a MEF2-interacting domain and a potent transcriptional activation domain (11). The C-terminal tail...

Interacting JNK-docking Sites in MKK7 Promote Binding and Activation of JNK Mitogen-activated Protein Kinases

“…MEK1, MEK2, MKK3, MKK4, and MKK6 have single D-sites in their N termini (38 -40, 44). MEK5 does not have a D-site but has a different MAPK-docking site of acidic character (41). Finally, as shown herein, MKK7 has three low affinity D-sites.…”

“…MEK5 does not contain a D-site but instead contains a novel MAPK-docking site of acidic character (41). No MAPK-docking site has heretofore been identified in MKK7; however, the N-terminal domain of the MKK7␤ isoform (the most prevalent isoform in humans) has been shown to be necessary and sufficient for high affinity complex formation with JNK1 (47,48).…”

“…This paradigm of MAPK recognition was first established for the yeast MEK Ste7 (36 -38) and has since been extended to mammalian MEK1 (38,39), MEK2 (38), MKK3 and MKK6 (2), MKK4 (40), and MEK5 (41). The MAPK-docking sites in many MKKs, including yeast Ste7 and human MEK1/2, MKK3/6, and MKK4, share a core consensus sequence consisting of a cluster of about three basic residues, followed by a short spacer of 1-6 residues, and finally a hydrophobic-X-hydrophobic submotif (Fig.…”

Activation of extracellular signal-regulated protein kinase 5 downregulates FasL upon osmotic stress

“…Cell viability was quantified by luciferase activity following transfection with the pCMV luciferase plasmid. 37 …”

QUIRKY interacts with STRUBBELIG and PAL OF QUIRKY to regulate cell growth anisotropy during Arabidopsis gynoecium development

“…These complexes, depending on their composition, ensure the specificity and fidelity of a variety of biological events such as cell polarity, but also cell signalling (Moscat et al, 2006;Nakamura et al, 2010;Terasawa et al, 2001;Wilson et al, 2003). Most, but not all, of the proteins involved in such signalling platforms interact via their PB1 domains, and PB1-containing proteins also interact with proteins that do not contain PB1 domains [for example, ERK5 (Nakamura and Johnson, 2007;Seyfried et al, 2005)]. Accordingly, POQ may therefore promote the formation of a multiprotein complex involved in cell signalling through the SUB Receptor-like kinase.…”